This protocol will test 2 hypotheses: 1) pulmonary macrophage activation as assessed by interleukin-8 mRNA production is increased in acute respiratory (failure (ARF) that progresses to the adult respiratory distress syndrome (ARDS) compared to macrophage status in ARF that does not progress to ARDS; and 2) pulmonary macrophage activation correlates with age in ARF potentially contributing to the increase in ARDS w/ age observed in the pediatric population.